Calanoids can be distinguished from other planktonic copepods by having first antennae at least half the length of the body and biramous second antennae.[2] Their key defining feature anatomically, however, is the presence of a joint between the fifth and sixth body segments.[3] The largest specimens reach 18 millimetres (0.71 in) long, but most are 0.5–2.0 mm (0.02–0.08 in) long.[2]